Recently we found one performance bug when doing network test with VTd
assigned devices - in some extreme case, the network performance in HVM
using new Linux kernel could be 1/20 of native. Root cause is one of our
sync-tsc-under-deep-C-state patches brings extra kilo-TSC drift between
pCPUs and let check-tsc-sync logic in HVM failed. The result is the
kernel fails to use platform timer (HPET, PMtimer) for gettimeofday
instead of TSC and brings very frequent costly IOport access VMExit -
triple per one call.

We provides below 2 patches to address the issue:

tsc1.patch: Minimize the TSC drift between pCPUs by letting BSP/AP set
TSC at the same time in time_calibration_rendezvous(). Looping a few 
times before writing tsc sounds better, but it may be too costly.
Signed-off-by: Xiaowei Yang <xiaowei.yang@intel.com>

tsc2.patch: only do TSC-sync if really necessary, which narrows its 
effect a lot.
Signed-off-by: Wei Gang <wei.gang@intel.com>


Thanks,
Xiaowei